Method of producing thin threads from polyvinyl alcohol and its water-soluble derivatives



June 29, 1943. H

P. SCHM-ITZ 2,322,976

METHOD OF PRODUCII XG THIN THREADS FROM POLYVINYL ALCOHOL AND ITS WATER-SOLUBLE DERIVATIVES Filed Oct. 18, 1940 ATTORNEY Patented June 29, 1943 METHOD OF PROD FROM POL UCING ram 'rnnnans YVINYL ALCOHOL AND ITS. WA-

TEE-SOLUBLE DERIVATIVES llilger Peter Sclunltz, Munich, Germany; vested in the Alien Property Custodian Application October 1 In Germany As is known, it is difiicult to produce very thin threads accordingto the usual spinning processes even if materials are employed well suited for being spun. Even under the most favorable conditions the spinning is difiicult because spinning solutions of a considerably high concentration must be applied in order to avoid the non-solidified thread being broken during the removing from the nozzle. Therefore a complicated spinningapparatus, high pressur and in many cases high temperatures must be applied.

The manufacture of very thin threads of polyvinyl alcohol and its water-soluble derivativesthat means of substances of which it was originally not known that they couldbespun and which only after 1931 could be worked up into thick threads according to the usual spinning methods-has been an unsolved problem until now. Ex-

periments in this direction have always shown that the thick threads obtained by the usual processes for spinning cannot be extended to considerably thin ones without breaking and that on the other hand diluted solutions cannot be worked up according to the usual spinning processes. These failures are meant to be due to the solvent water which is alone appliable in practice,.be cause polyvinyl alcohol has a high capacity for binding water.

It has now been found that also relatively diluted aqueous solutions of polyvinyl alcohols and their still water soluble derivatives may be worked up into very thin threads very resistant to tear and which may be obtained even thinner than the elementary filament of natural silk if these solutions are conducted in a thin jet through a suit- 8, 194., Serial No. 361.796

November 3, 1m 5 Claims. (Cl. 18 -54) which the pohrvinyl alcohol is extruded. The filaable nozzle upon a support which is in a rela-.

tive movement against the falling liquid jet. Principally, it is all the same whether the nozzle or thesuppprt is moved. The support may consist of a continuous band moving under the nozzle or of a disk rotating under it or a disk over which the nozzle is moving in a circle, and the like. The support in form of a rotating drum is of a technical advantage. The liquid jet falls upon such a drumparallel to the rim of the drum and the forming thread is transported by the rotating drum, provided that a sufficient amount of liquid continuously leaves the nozzle. If the drum is wished to rotate more. rapidly a raised pressure may be applied upon the liquid which is to be workedup in order to avoid that the thread breaks.

One modification of the invention is illustrated in the accompanying drawing in which Figure 1 is a diagrammatic side elevational View ments 6 extruded from the several nozzles. pass vertically downward into tangential contact with the drum 1 which rotates in the direction of the arrow. The filaments are carried into contact with the bath 8 in container 9. The filaments 6 then pass over roll it, and they are then guided by means of traverse bar II on to the filament support I! which may be driven by surface drive roller l3.

This method of producing threads is known but until now it was proposed only for materials easily to be spun and this method has not been proved to be well appliablein the art. On the other hand it could not be recognized that this method is even appliableto diluted solutions and especially to low concentrated aqueous solutions of thread-forming materials. Above all, it is surprising that by this way polyvinyl alcohol-which,

I as is known, is not wel1 suited for spinning processesmay be worked up into thin threads at all, and it is especially surprising that thereby diluted aqueous solutions of this substance may be spim into thin'threads.

The advantages of this method'are as follows: 1 it is not only possible to produce thin threads but thereby may be also applied diluted solutions produced and casted at usual temperature, whereby the known undesired hardening-effect of heat up- I on polyvinyl alcohol can be avoided.

By this method of casting threads, a little stretching anddiminishing of the diameter of the free-suspending liquid-thread may be also attained before it reaches the support. on the other hand the pre-stretching of the thread and other influences upon it may be promoted by subjecting the free-suspending thread to methods changing the consistency of the thread, especially the viscosity or solidifying the surface of it in a more or less degree, e. g. removing the solvent by means of a current of gas or heating the thread or cooling the warm casted thread. Also the influence of tanning orcondensing gases like aldehvde's may be applied.

In every case, however, the selected methods must be applied in such a manner that the liquid- Jet reaches the support in a somewhat liquid state. The solidification of the thread is attained upon the rotating drum by one of the above mentioned methods or by a combination of them. The solidi'iication is preferably effected by drying by means of a current of air or otherwise the under parts of the drum may be passed through a bath which has a precipitating, tanning, vulcanizing or condensing eflect upon the thread, whereby the bath-liquid may be removed later on and the thread be dried by a current of air. There are for instance alcohol or solutions of vdichromates or solutions of Congo red as described in Patent 2,125,374 which are suitable for this purpose.

If necessary, tanning-, condensation-, and vulcanisation-agents may already be added to the solution to be casted. It is also possible to add liquids promoting the evaporation of water such as acetone, alcohol, suitable amounts of acetic ester and the like. I

The efficiency of the solidifying method must be adjusted to the given casting solution, to the desiredwidth of the nozzle and to the velocity with which the solution leaves the nozzle, whereby the size and the rotation-velocity of the drum must be taken into consideration. I

Generally it is not necessary that the thread is already solidified completely upon the drum; it is suflicient if an approximate solidification is attained, by which it is possible to remove the thread from the drum when it has passed the largest compass of the drum.

The removing of the. thread from the casting support is preferably executed by applying the methods known in the usual processes for spindrawn ofi from the drum near the testing device and runs over a roll an'anged' near the casting device but above the vertex of the drum. Generally the drawing oil! of the thread is not difficult. In special-cases the taking away of the thread may be facilitated by a current of air which is blown against it. Generally a twistling of the thread by torsion and/or a stretching of it which is-grad'ually executed if necessary and which must be adjusted to the material of the thread is combined with the reeling. A spinning and twistling together with other threads may also follow immediately and so on.

The threads drawn of! from the drum or from another casting support may be subjected to a suitable after-treatment during or after the drawing off, e. g. to a further drying, heating", tanning, condensation, dyeing, loading, delusterizing, roughening, sizing, and soon. An excessive amount of softeners incorporated to facilitate the stretching of the thread may be subsequently rei moved more or less by solvents which solve well the softener agents without solving the material of the thread.

The new method allows also the working up of casting solutions containing fillers, pigments, agents for delusterizing, f. i. titanium dioxide or usual loading agents, in a sumcient finedistribution. Softeners, stabilizers, dyestuffs and the already above named agents promoting th solidification and if necessary catalysts promoting the further polymerization may also be added.

According to this method also threads may be produced containing included gas. Even hollow threads may be obtained. The manufacture of the threads upon the moved casting support and their drawing oil may even be executed if casting solutions are worked up containing an emulsified amount of gas or it hollow spaces are P OQ Q Q in the casted threads by solidifying at first only their surfaces and heating the threads subsequently-while they are still upon the drum or of the thread.

The leading of the solidifying threads by a rotating roll is so exact, that upon the roll a series of threads may be casted out of nozzles lying closely adjacent. Several hundred threads may be produced upon a drum of only 1 m. axis-length at the same time.

Following a suitable casting solution:

Example Parts by weight Polyvinyl alcohol (high or low viscous).. Glycerin or ethylene glycol 0.25 Water g 94.75

By this specially careful production of threads of polyvinyl alcohol and by the now attainable thinnest formation of the elementary threads for twisted yarn, new possibilities are given for promoting the resorption of threads being used for surgical purposes.

I claim:

1. The method of producing thin threads of polyvinyl alcohol which comprises casting a. di-

lute aqueous solution, containing of the order of 5% of polyvinyl alcohol through a nozzle, in the form of a thread, upon a rotating drum, solidifying said thread on said drum. and drawing the solidified thread from the drum.

2. The method of producing thin threads of polyvinyl alcohol which comprises casting a dilute aqueous solution, containing of the order of 5% of polyvinyl alcohol .through a. nozzle, in the form of a thread, upon a rotatingdrum, drying and solidifying said thread on said drum, and drawing the dry, solidified thread from the drum.

of polyvinyl alcohol, through a nozzle, in the form of a thread, upon a rotating drum, stretching said thread on said drum, drying and solidifying said stretched thread on said drum, and drawing-the dry, solidified thread from the drum.

4. The method of producing thin threads of polyvinyl alcohol which comprises casting a dilute aqueous solution, containing of the order of 5% of polyvinyl alcohol, through a nozzle, in the form of a thread, upon a rotating drum, imparting a suflicient velocity of rotation to said drum to stretch said thread, drying and solidifying said thread on said drum, and drawing the dry, solidified thread from the drum.

'5. The method of producing thin threads of polyvinyl alcohol which comprises casting a dilute aqueous solution, containing of the order of 5% v of polyvinyl alcohol through a nozzle, in the form 

